1. Field of the Invention
The present invention relates to pacing lead assemblies and more particularly to a screw-in pacing lead assembly having a corkscrew shaped securing device at the distal end thereof which is adapted to be threaded into living tissue for securing an electrode assembly at the distal end of the pacing lead to the living tissue such as to the endocardium in a ventricle or atrium of the heart.
2. Description of the Prior Art
Pacing lead assemblies have been in use for a number of years for supplying electrical stimulation pulses to or for receiving electrical pulses from living tissue. Such pacing lead assemblies have included a pacing lead comprising single or multiconductor coils of insulated wire having an insulating sheath thereabout with the lumen or cylindrical envelope defined by the coiled wire providing a space into which a stiffening stylet can be inserted. The conductive coil is connected to an electrode in an electrode assembly at the distal end of the pacing lead and typically a terminal member is mounted within a flexure sleeve at the proximal end of the pacing lead assembly and connected to the proximal end of the conductive coil.
A stylet is inserted into the pacing lead to provide stiffening of same when it is inserted into a vein for positioning the lead in living tissue such as in the endocardium in the ventricle or atrium of the heart or proximate thereto.
After the electrode assembly with an electrode at the tip thereof is positioned at a desired location within the heart it is desirable to provide some form of means for securing the electrode assembly at that location. One such means for securing the electrode assembly in place is a corkscrew (or helical) shaped securing device which is mounted at the distal end of the pacing lead assembly. Typically a proximal end of the corkscrew shaped securing device is fixed in a mounting member and the outer end thereof is adapted to be screwed into living tissue. In one such screw-in pacing lead assembly, a stylet with a specially configured distal end, such as a screwdriver shaped end, is adapted to be received in a mating slot in the rear end of the mounting member. Then the proximal end of the stylet is rotated within the pacing lead to cause the corkscrew shaped securing device to advance into living tissue.
This type of pacing lead assembly requires a stylet with a specially configured head. Also in this type of pacing lead assembly the stylet must be inserted all the way to the distal end of the pacing lead, properly located within a mating slot and then rotated to cause the corkscrew shaped securing device to be screwed into living tissue.
An example of such a screw-in pacing lead assembly is disclosed in U.S. Pat. No. 4,217,913 issued on Aug. 18, 1980 to Robert C. Dutcher and entitled BODY-IMPLANTABLE LEAD WITH PROTECTED EXTENDABLE TISSUE SECURING MEANS. Here the helix or corkscrew can be electrically insulated from the electrode or electrically coupled thereto as provided in an earlier screw-in-lead assembly disclosed in the Bisping U.S. Pat. No. 4,106,512.
Although such screw-in pacing lead assemblies have functioned adequately in the past, certain problems have been encountered with same. First of all, due to the non-linearity of a vein and the chambers of the heart, the stylet does a straight path to the mounting member at the distal end of the pacing lead. Rather it has a bowed or curved configuration within the lead. Accordingly, when the stylet is rotated, it tends to cause the pacing lead to move against the side wall of the vein or chamber of the heart in which it is located possibly causing trauma to the vessel or heart wall.
Also, the screwdriver shaped head at the distal end of the stylet has sharp edges which can damage the multiconductor coil in the lead as the stylet is moved through the coil. The head of the stylet also can catch on a turn of the coil and pierce through the insulating sheath.
Furthermore, such a screw-in pacing lead assembly requires that the distal end of the stylet be firmly located within a slot in the mounting member mounting the corkscrew shaped securing device. This is sometimes difficult to do and a physician manipulating the proximal end of the style is not always certain that he has effectively engaged the screwdriver shaped head of the stylet with the slot in the mounting member thereby to screw the corkscrew shaped securing device into living tissue.
It has also heretofore been proposed to provide a retaining coil at the end of an electrode system inserted into the vagina for monitoring fetal heartbeat in U.S. Pat. No. 3,827,428 issued to Edward H. Hon, et al. on Aug. 6, 1974 and entitled ELECTRODE STRUCTURE FOR MONITORING FETAL HEARTBEAT AND THE LIKE. In this electrode system for monitoring fetal heartbeat, a curved guide tube is adapted to be inserted through the vagina and cervix of a woman in labor. Then, a retaining coil mounted at the distal end of a holder mounted on the end of flexible driving tube within the guide tube can be rotated by rotating the driving tube to screw the retaining coil into living tissue. Two twisted leads are received within the flexible driving tube and extend from the retaining coil holder at the distal end thereof to the proximal end of the flexible driving tube received within the guide tube.
As will be described in greater detail hereinafter, the screw-in pacing lead assembly of the present invention provides a drive means receivable within a conventional pacing lead and fixed at the distal end thereof to a mounting member mounting a corkscrew shaped securing device and at its proximal end to a drive member. The drive mechanism defines a cylindrical envelope or lumen through which a stylet can be inserted for stiffening of the pacing lead when required but which stylet is not utilized in rotating the corkscrew shaped securing device into living tissue and which stylet can have a rounded distal end to facilitate insertion thereof into and through a pacing lead.